1. Field of Invention
This invention relates to anti-wetting ink jet nozzles and a method of precisely forming anti-wetting ink jet nozzles. One method uses laser ablation and another method uses precision injection molding to create a nozzle with a lip that can prevent unwanted deflection of ink droplets. The ink jet nozzles can be made from materials that avoid damage from inks which have been known to cause damage to nozzles made from silicon wafers or semiconductors. Moreover, the invention enables a wider range of inks, e.g., abrasive or aggressive inks in the upper and lower pH ranges, for use with ink jet nozzles.
2. Description of Related Art
FIG. 1A shows a prior art ink jet printing device 1 having a conventional nozzle structure that includes an annular bore 3 and a front face 4 that is oriented perpendicular to the axis of the bore 3. Each bore 3 of an ink jetting device 1 is supplied with a supply of ink 2 that is intended to create characters on a recording medium (not shown). FIG. 1A shows the progression of ink 2 as it emerges from the bore 3 and eventually onto a recording medium. The formation of a droplet 5 eventually occurs at the mouth of the bore and gradually builds in size until the ink emerges from the bore and prints the desired character on the recording medium. Thermal ink jet devices of this type suffer in print quality when wetting 6 occurs on the front face 4 of the ink jet nozzle. This type of wetting creates imprecise character printing and often times smudging.
In addition, when a portion 7 of the ink 2 surrounding the orifice 3 dries in an asymmetrical manner as shown in FIG. 1B, a next forming droplet 8 is cohesively attracted to the side where the wetting is greatest and deflected in that direction as indicated by arrow 9. Prior art thermal ink jet devices use a hydrophobic front face coating to minimize front face wetting by the ink in an attempt to avoid these directionality problems.
Another solution is to minimize wetting by microfabricating a nozzle structure surrounding the orifice that minimizes front face wetting. Such a solution to the ink wetting problem is shown in prior art FIG. 2 which shows an ink jet nozzle 10 having a front face 11 perpendicular to a bore 12 forming a passage for ink 13 to be supplied from an unshown source. In addition, the nozzle 10 of FIG. 2 includes a lip portion 14 that serves to prevent wetting on the front face 11 of the nozzle. While this nozzle structure helps to eliminate wetting, it suffers because it is currently manufactured by expensive chemical or mechanical processes.
FIG. 3 shows a five-step chemical process by which a lip portion of the prior art device of FIG. 2 is formed. The first step is to provide a brass plate 15 as shown in step (a) and to drill a first cylindrical hole 16 and a second countersunk bore 17 within the brass plate 15 (step (b)). In step (c), a layer of nickel 18 is applied by the xe2x80x9celectrolessxe2x80x9d method to all surfaces of brass plate 15 of step (b) including top face 19, bottom face 20, and the surfaces of throughhole 16 and countersunk hole 17. In step (d), the bottom surface 21 of the nickel layer 18 and some of the brass, where necessary, are removed by grinding. Finally, in step (e), the surface 20 surrounding the nickel surface 18b coated onto annular bore 16 is selectively etched to produce a lip portion 14 of the nozzle.
FIGS. 4A and 4B show an alternative method for mechanically forming a lip portion on an ink jet nozzle. In this process, the object is to punch a hole using punch 22 in a nickel plate 23, the nickel plate forming the nozzle. A force F drives the punch 22 into the nickel plate 23. At the end of the process, a part of the nickel plate 23 will penetrate into a plastic strip 24. Because of the supporting action of steel plate 25 and the fluid behavior of plastic 24, a hole 26 without burrs and of the desired shape including a lip 27 is produced in the nickel plate 23.
It is also known to produce nozzle plates using a laser ablation technique, whereby a laser is used to create a bore, e.g., a countersunk bore, through the nozzle plate. However, such nozzles also suffer from the ink wetting problems described above because they do not have a lip portion, as shown in FIG. 2.
U.S. Pat. No. 4,961,821 to Drake et al. discloses a method for forming throughholes in silicon wafers using an orientation dependent etching technique, and is incorporated herein by reference. As shown in FIGS. 9E and 9F of Drake, however, the ink jet nozzles encounter the same problems as those discussed in reference to FIGS. 1A and 1B. Moreover, the orifices of Drake do not provide for a lip portion that prevents wetting around the area surrounding the ink jetting orifice. In addition, the method for manufacturing the orifice includes an anisotropic method of etching that requires surfaces 31 and 32 to be covered with an etch resistant layer 34 in those areas where it is not desired to form a throughhole. Moreover, Drake anisotropically etches (100) crystallographic planes 35 and 36 using an additional etch resistant layer 34 to mask those portions of the wafer 30 not desired to be etched.
U.S. Pat. No. 5,487,483 to Kubby, incorporated herein by reference, discloses an ink jet nozzle and a method for manufacturing the same. A hollow extension lip is provided to prevent unwanted deflection of ink droplets. The nozzle as well as the hollow extension lip are disclosed as being made, for example, using a two step process including physical sputter erosion and chemically etching the nozzle area surrounding the orifice using an anisotropic etching method. However, this process is limited for use with silicon wafers or other semiconductor materials. Also, silicon/semiconductors are limited because acidic or basic inks can cause damage to those materials, and thus the selection of inks for use in ink jet nozzles using such materials is limited.
It is an aspect of the present invention to provide an anti-wetting ink jet nozzle for a printing device that prevents unwanted deflection of ink droplets by preventing asymmetrical depositing of ink about the regions surrounding the orifice of the ink jet nozzle.
It is another aspect of the present invention to expand the materials available for producing anti-wetting, precision ink jetting nozzles. For example, the manufacturing processing techniques can be used to create nozzles made, for example, of polymers (e.g., polysulphone), plastics, Teflon(copyright), metals and/or oxides, etc.
It is another aspect to form the nozzles of the ink jetting devices in a cost-efficient and time-efficient manner, and which can eliminate the problems associated with ink selection limitations and ink history defects. Thus, more chemically aggressive inks can be used, e.g., inks having a pH of 3 or 9-10.
According to one aspect of the invention, there is provided a method of microfabrication of an ink jet nozzle. The method comprises the steps of providing a nozzle plate having an upper surface and a lower surface; laser ablating the upper surface of the nozzle plate to create a bore which extends from the upper surface of the nozzle plate to the lower surface of the nozzle plate; and laser ablating the lower surface of the nozzle plate to create a lip which extends away from the lower surface of the nozzle plate.
According to another aspect of the present invention, there is provided a method of microfabrication of an ink jet nozzle. The method comprises the steps of providing upper and lower molds forming therebetween a space defining a shape corresponding to an ink jet nozzle having a nozzle plate and a lip formed in one piece with an extending away from the nozzle plate; injecting the space with a molding material; and removing the upper and lower molds to release the thus formed ink jet nozzle. In this method, the molding material may be a polymer, a plastic material, ceramics, or any material that can be injection molded. In addition, the method may further comprise forming the lip of an ink jet nozzle using a nozzle forming pin which may be formed in the upper mold. In addition, the pin may be movable with respect to both the upper and lower molds to enable manufacturing nozzle plates and corresponding lips with different shapes and characteristics.
In accordance with another aspect of the present invention, there is provided an ink jet nozzle comprising a nozzle plate having an upper surface and a lower surface; a lip formed in one piece with the nozzle plate and extending away from the lower surface thereof; and a bore extending from the upper surface to the lower surface of the nozzle plate and completely through the lip. The bore has an interior surface inclined at an angle with respect to the upper and lower surfaces, the angle being substantially constant throughout the nozzle plate and the lip.
In embodiments, a cross sectional shape of the lip may be trapezoidal, a lower surface of the lip may form an acute angle with the interior surface of the bore, the nozzle plate and lip may be made from a material resistant to ink latitude limitations an ink history defects, and/or the material may be a plastic and/or polymer.
These and other aspects of the present invention will become apparent from or described in the following detailed description of preferred embodiments.